An electromagnetic actuator for operating a setting member has an electromagnet energized by a controllable current supply. The magnetic force resulting from the energization of the electromagnet affects an armature which is coupled to the setting member to be operated. Usually a resetting spring is provided which, in the de-energized state of the electromagnet, holds the armature--and the setting member connected therewith--in a first switching position. The armature, upon energization of the electromagnet, is moved towards the second switching position by the magnetic forces and is held in such a second switching position as long as the electromagnet is in an energized state.
For affecting the velocity of the armature as it approaches the pole face of the electromagnet and also, as the armature moves away from the pole face after de-energization of the electromagnet, a rapid change in the magnetic force is a desideratum. Such a rapid force change, that is, a rapid change in the magnetic field, however, is opposed by eddy currents. Conventionally, the generation of eddy currents in the electromagnet may be minimized by making the yoke body of a stack of sheet metal laminae. Thus, the energization of the electromagnet, especially during a phase when the armature is still at a significant distance from the pole face, results in a rapid build-up of the magnetic field, as described in German Offenlegungsschrift (application published without examination) No. 35 00 530. During the terminal phase of the approach of the armature, however, the effect of the electromagnet is influenced by the armature to an increasing extent. Since the armature is, as a rule, made of solid iron, the eddy currents generated therein work against a rapid field change and thus oppose a rapid change of the electromagnetic force. The same phenomenon occurs as the armature moves away from the pole face. While upon de-energization of the electromagnet only small eddy currents are present in a laminated yoke body, the eddy currents which flow in the solid iron armature even after a de-energization of the electromagnet, delay the release of the armature from the pole face. Such a "sticking" of the armature to the pole face leads to disadvantages in case of high switching frequencies and adversely affects a reproducible control of the setting member.